Biogeochemical cycling of Mn and Fe in an area affected by eutrophication:The Adriatic Sea

Measurements of dissolved Mn and Fe and total particulate Mn, Fe and Al wer e made on seawater samples collected in the Northern Adriatic Sea in differ ent seasons (May 1994, June-July 1994, September 1994 and February 1995), a nd in the Central Adriatic Sea in June-July 1994. Porewaters were also anal ysed for dissolved Mn and Fe in February 1994, June 1994, September 1994 an d February 1995. Seasonal observations of dissolved Mn and Fe and particulate excess Mn and Fe in the Northern Adriatic Sea have demonstrated pronounced temporal and s patial variability of their distribution. This variability was mainly due t o: (a) storm events which broke down stratification of the water column and enhanced resuspension and advective transport of particulate forms, and (b ) fluctuations of oxygen concentrations in the water column and sediment-wa ter interface, related to the biodegradation of the organic matter produced during bloom periods. Large inputs of dissolved Mn and Fe were attributed to reductive solubilization and diffusion from the sediment-water interface . Particulate excess Mn and Fe concentrations were also increased by oxidat ion in the presence of oxygen of dissolved Mn and Fe, which had diffused fr om the sediment-water interface. (C) 2000 Academic Press.